1. Field of the Invention
The present invention relates to an electric double layer capacitor.
2. Discussion of the Background
The materials for the current collectors and for the casings for accommodating capacitor-constituting elements for electric double layer capacitors have been disclosed, for example, in Japanese Unexamined Patent Publications No. 44461/1975, No. 44464/1975, No. 206116/1983 and No. 263418/1985.
However, such electric double layer capacitors have problems such that when e.g. aluminum or stainless steel is used as the material for the current collectors or casings which are in contact with an electrolyte solution, such material partially undergoes dissolution without being anodized completely to a passive state. In addition, aluminum has less mechanical strength than conventional stainless steels and is not suitable for current collectors or casings. Likewise, when a valve metal such as titanium or niobium is used, corrosion due to the anodic dissolution takes place if the charging is conducted at a high voltage, and accordingly, the rating for the working voltage of the capacitor had to be set at a low level.